U.S. Pat. No. 3,685,345 issued in 1972 to H. L. Wise describes a soil-gas sampling device and method therefor. The Wise device requires that a bore be drilled in the ground, and thereafter it be sealingly plugged with a suitable cover, to prevent air infiltration in the bore. An inlet pipe and an outlet sampling pipe extend through the cover into the ground bore, both pipes being connected to a pump. A circulation fluid (or fluid vector) is pumped through the inlet pipe, so that it comes into repetitive contacts with the bottom portion of the surrounding earth formation. The outlet pipe recovers an equal amount of fluid, and concentration data concerning a selected fluid may be acquired from the outlet fluid thus retrieved, by known means.
Wise teaches that the relevant information concerning the soil condition will be obtained when the rate of change of the concentration of the selected fluid repetitively exposed is low relative to its rate of change in the early stages of the fluid circulation. Thus, Wise offers a method for testing soil in which the concentration of the fluid in the earth formation is evaluated by means of a fluid vector.
An important disadvantage of the Wise method is that a bore has to be drilled into the ground for the testing to be accomplished. This step prolongs the whole operation significantly, and the total boring time may become very significant where many fluid concentration readings have to be accomplished in a single site. Moreover, if the site would have to be tested deeper into the soil, then the boring operation would become proportionally longer.
Another important disadvantage of the Wise method is that the results obtained thereby give the concentration of the selected fluid in the soil. This is disadvantageous especially if the Wise method was to be used to evalutate a soil contaminated by an hydrocarbon or a chlorinated solvent. The concentration of a selected fluid in the soil does not necessarily give a direct relationship with the concentration of the contaminant in the area. Fluid contaminants migrate in porous soil, which can lead to erroneous positive contamination results. This migration is influenced by many parameters such as the nature of the soil (its porosity, organic content, moisture content, . . . ) and the nature of the contaminant. Indeed, the relative presence in a sample of the volatile or gazeous contaminant does not necessarily indicate its proximity to the pollution since migration can and does occur. The spreading or extension of the contamination near underground fuel supply tanks, for example, cannot be determined efficiently by the Wise method, which will provide the concentration of the vapor or gazeous contaminant fluid in the soil by means of the circulation of its vector fluid.